Relative units figure
Merge pull request #41 from nwtn/gh-pages

Relative units figure
Added simpler images to represent DRP and viewport
Cleaned up text
Added description of src-n as proposed solution
Resized image. It was too huge.
New image showing viewport selection
renamed resolution selection.
source file for resolution selection.
Added Resolution-based selection section.

+ small fixes
Acknowledged @tabatkins and Paul Robert Lloyd
Fixed markup
Merge branch 'usecases-fixup' of https://github.com/ResponsiveImagesCG/ri-usecases into usecases-fixup

Conflicts:
	index.html